Two Brooklyn sixth-graders were busted at school yesterday after they were caught playing with a loaded handgun – which one of them brought for show-and-tell, authorities said.

A boy had concealed the deadly weapon in his backpack and took it out to show a classmate as they sat in the cafeteria of Roy Mann JHS 78 in Bergen Beach. They are both 12.

A student spotted the boys toying with the .45-caliber semiautomatic and reported it to school officials around 11 a.m.

NYPD school safety agents confronted the two students and took them away to be questioned separately.

The armed student allegedly told school officials the gun belonged to a friend of his father – and he had brought it to school for show and tell, a source said. The second student was found carrying two bullets.

Police led the two boys off in handcuffs. A Board of Education spokesman said they were suspended.

About two hours later, police summoned Roger Stewart, 47, to the 63rd Precinct. He was charged with criminal possession of a weapon and reckless endangerment for failing to secure the weapon, police sources said.

Stewart is a friend of one of the two boys’ parents, the sources said.

An eighth-grade girl said that the gun-toting pupil was in a special education class.

“I don’t think he knew what he was doing,” she said.

A sixth-grader said he didn’t know who the two boys were.

Because the boys are minors, their names were not released.

It’s not the first time a student has been caught bringing a loaded gun to school this year.

In February, a 13-year-old girl was caught carrying her dad’s loaded gun into her Ozone Park, Queens, school.